unless you need to press more than 6 keys at once, yes it's perfectly fine...

I heard there is a lag associated with a USB keyboard.

Polled at whatever hz the port is set at.

I am not exactly sure how it works. I have a Zowie EC1 eVo. My polling rate is 1000hz already. If I do a hz hack, will it go to 2000hz? Or because it is already operating at 1000hz, will the keyboard work at the same hz because the mouse is the same hz?

That's on a port by port basis so you'd have to do it manually I guess.

No. You can not get 2000hz polling on a usb 2.0 port. It can only poll at 1000hz. usb 3.0 works differently but there is no hardware that I know of that takes advantage of this yet.

cooller uses usb

What does he use specifically?

A coolermaster keyboard. Yep.

USB keyboards are fine to play on.

Can I assume that the USB keyboard is just as responsive as a USB mouse?

the newer ones for sure, the older ones are often having some limitations on there... but in general nowadays usb is as fast and better than ps2.

Although the concept behind ps2 is imo nicer for input devices....